1) Put your oven on broil.
2) In a medium bowl mix the olive oil, black pepper, oregano, Italian seasonings and lemon lemon juice. Put the mushroom in the mixture and coat them with the mixture and set aside for 10 minutes.
3) While the mushrooms are marinating, spray a medium-sized pan with cooking spray (or you can use olive oil) and saute the onions until there brown.
4) After the mushrooms are done marination place them in a pan and make sure there spread out and put them in the oven for 4 minutes and then flip them over and cook them for another 4 minutes.
5) Slice open the ciabatta bread and place Swiss cheese slices on one side of it. Put it in the broiler until the cheese is melted. Dig out the bread on the side without cheese and place the mushrooms and onions inside the dug out side. ENJOY!!!
Source of recipe: My neighbor gave me this recipe